Mid-Miocene tectonic development of the Palawan orogenic wedge

The Palawan collision has for long been inferred from the regional geological record. However, precise constraints on the timing of major orogenic growth is limited, relying mostly on variably available biostratigraphic dating of the erosive products in the surrounding offshore basins. Here, we present new thermochronologic dating results constraining the tectono-thermal evolution of the continental affinity basement units of the Palawan orogenic wedge. Our results indicate a very consistent timing of a major exhumation phase at 14.9 ± 0.5 Ma (weighted mean of seven samples’ zircon fission-track pooled ages) recorded in the Cretaceous meta-sediments of the Northern Palawan island. The exhumation event is synchronous to a major erosive phase with the initiation of clastic sedimentation and a major increase in sedimentation and subsidence rates recorded during the deposition of the Pagasa Fm. and equivalent units in the adjacent basins. It is also contemporaneous to convergence and thrusting described offshore in the Central and Southern Palawan Trough and the NW-Sulu Sea. We interpreted this exhumation phase as resulting from a major crustal thickening and erosive phase associated to the collision between the proximal Palawan margin and the Cagayan volcanic arc after complete subduction of the Proto-South China Sea oceanic crust. This collisional episode appears to be distinct from the younger and still active transpressive orogen of the Philippine Mobile Belt.